Abstract

In this paper, the rheological characteristic of HPAM solutions is studied and the oil displacement efficiencies of viscous-elastic HPAM solutions (concentration in series) and viscous glycerin solutions (no elasticity, viscosity in series) are studied by flooding at visual microscopic glass models and artificial cores. Also, the effect and mechanism of the viscous-elastic behavior of HPAM solutions and glycerin solution on the displacement of residual oil films under mixed wettability conditions is studied, the relationship between the elastic behavior of HPAM and oil displacement efficiencies is given. The results of rheological characteristic measurement indicate that both the viscosity and the first normal stress differential (N1) of HPAM solutions increase with the increase in concentration, HPAM solutions show strong viscous-elastic characteristics under high concentration conditions. The results of microscopic oil displacement experiments indicate the displacement efficiencies of HPAM solution flooding and glycerin solution flooding gradually increase with the increase in the viscous-elastic behavior of HPAM solutions and the viscosity of glycerin solutions. However, for HPAM solution flooding, the displacement efficiency is always higher and residual oil saturation lower than that of glycerin at the same viscosity and same capillary number. Last, the displacement experiment in artifical cores is conducted and the similar resultes are validated.

Introduction

In the field of petroleum engineering, it has long been believed that the mechanism of polymer flooding in Enhanced Oil Recovery (EOR) is mainly to improve the mobility ratio and macroscopically increase the sweep efficiency[1] and another main accepted mechanism of mobilizing residual oil after water flooding is that there must be a rather large viscous force perpendicular to the oil-wet interface to push the residual oil, this force must overcome the capillary forces retaining the residual oil, move it, mobilize it and recovery it[2].In the last few years, the conclusions of some papers[3–7] indicate the viscous-elastic behavior of HPAM (partially hydrolyzed polyacrylamide) solutions can enhance the oil displacement efficiency. Wang Demin[3–4] puts forward the major mechanism of polymer flooding increasing the micro-scale displacement efficiency is that the flow pattern and magnitude (value) of the viscous force parallel to the oil-water interface caused by the flow of viscoelastic fluids in porous media is different than for Newtonian fluids. This difference is the main cause of the increase in oil displacement efficiency for viscoelastic fluids flowing in porous media. Different polymer fluids had quite different elastic properties. The difference in incremental recovery can be more than 6%OOIP (original oil in place), which is substantial, it can make a polymer flood successful or not. Up to the present, papers about the separate effects of viscous and elastic behavior each on oil displacement efficiency have not been published, i.e. the viscous and elastic behavior of HPAM solutions are not taken into account separately in flooding, the effect of elastic behavior of the HPAM solutions on oil displacement efficiency has not been described quantitatively. Therefore, study on the effect of the elastic behavior of HPAM solutions on displacement efficiency is very necessary.

Equipment, Material and Basic Step in Experiment

In this study, oil displacement experiment is conducted in simplified microscopic pore model that is etched in glass and in artifical core. For the microscopic oil displacement experiment, the images recorded in the process of oil displacement are translated into digital signal by the image collection system, the behaviors of microscopic oil displacement of HPAM and glycerin solution are analyzed through the image analysis technology.

Equipment

Microscopic Oil displacement equipment consists of displacement part, image collection part and image analysis system. The experiment equipment and flow chart is as Fig.1. The rheometer is made in Germany HAAKE Company and is used for analyzing the rheological behavior of HPAM solution.

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